The surface tension of a liquid and the interfacial tension between immiscible liquids are important thermodynamic properties. The most popular instrument used in practice is the tensiometer in which the force required to detach a ring or plate from an interface is measured. This technique is accurate but the equipment is expensive. Various other techniques have been patented, as set forth in U.S. Pat. Nos. 2,054,438, 2,654,243, 3,765,227 and 3,096,642, but none has been found to be entirely satisfactory.